I. Field of the Invention
The present invention relates generally to mail processing systems and, more particularly, to an anti-doubling detection and correction system for use in mail processing systems.
II. Discussion of the Background Art
Mail processing systems, such as mail sorters, typically include one or more feeders designed to singulate an individual mail piece from a stack of mail for downstream processing. FIG. 1 shows a top view of a mail feeder 100 for an automated mail sorting machine (AFSM) commonly used by the U.S. Postal Service. The mail feeder 100 includes a conveyor belt 102 with a horizontal run moving in a first direction A and a feeder plate 104 at a terminal end of the conveyor belt perpendicular to the horizontal run. Mail pieces M are stacked on edge in a generally vertical orientation on the conveyor belt 102 and moved in the first direction A toward the feeder plate 104. As the mail stack approaches the feeder plate 104, the leading mail piece at the front of the stack is dropped from the feeder belt and drawn against the feeder plate by vacuum ports 106 formed in the plate. The mail piece is then launched in a second direction B, transverse to the first direction A, by rotation of a perforated belt 108 looped through a pair of windows 110 on opposite sides of the vacuum ports 106 in the plate. Intermittent vacuum sources 112a and 112b behind the perforated belt 108 draw the mail piece against the belt to overcome friction between the leading mail piece and other mail pieces in the stack.
Often times a second mail piece is unintentionally pulled along with the first mail piece as a result of friction, electrostatic charges, adhesion, pressure or other forces acting on the mail stack. When two or more pieces are pulled into the sorting machine, the second piece is sorted based upon the destination of the first piece. This situation may not be detected until both mail pieces are much further in the mail delivery process, resulting in mishandling and additional cost to the customer for re-sorting. In an attempt to avoid this situation, current mail feeding technologies use some form of fixed anti-doubling mechanism 114 on one side of the mail to hold back mail pieces that are not intended to be fed into the sorting system while the leading mail piece is grabbed by rotating pinch wheels 116. However, existing anti-doubling mechanisms are not always effective and can damage certain types of mail, such as poly-wrapped, stapled and open mail.